Statistics Module 2

A new drug designed to prevent exacerbations of genital herpes undergoes a clinical trial. One hundred patients are given the new drug. During a three month period, 10 of the patients have an episode of genital herpes.

In the control group there are 300 patients who are given a placebo. In this group 50 people have an exacerbation during the same time period.

What is the relative risk of having an exacerbation of genital herpes whilst taking the new drug?

A cohort study is being designed to look at the relationship between smoking and breast cancer. What is the usual outcome measure in a cohort study?

Which one of the following statements best describes a type II statistical error?

Which one of the following statements regarding the power of a study is correct?

A study looks at the chance of having a myocardial infarction (MI) in patients with known ischaemic heart disease.

Group A are given standard treatment. After 5 years 20 of the 100 patients have had a MI.

Group B have standard treatment plus a new cardiac drug. After 5 years 10 of the 60 patients have had an MI.

What is the odds ratio of having a MI whilst taking the new drug compared to those who do not?

A study looks at whether golf actually increases the risk of medial epicondylitis. Sixty people who regularly play golf are matched to sixty people who do not play golf. Thirty of the golfers had developed medial epicondylitis at some point compared to ten of the non-golfers.

What is the odds ratio of developing medial epicondylitis for people who play golf?

Which one of the following statements regarding relative risk is correct?

A study is to be performed to assess whether the combined oral contraceptive pill is protective against pelvic inflammatory disease.

What is the most appropriate type of study design to provide robust evidence?

A new drug is trialled for the treatment of lung cancer. Drug A is given to 500 people with early stage non-small cell lung cancer and a placebo is given to 450 people with the same condition. After 5 years 300 people who received drug A had survived compared to 225 who received the placebo.

What is the number needed to treat to save one life?

A new blood test to screen patients for heart failure is trialled on 500 patients. The test was positive in 40 of the 50 patients shown to have heart failure by echocardiography. It was also positive in 20 patients who were shown not to have heart failure.

What is the positive predictive value of the test?

Which one of the following may be used to calculate the number needed to treat?

A study is performed looking at the chance of stroke in high-risk patients taking a new oral antithrombotic drug compared to warfarin. The following results are obtained:

What is the relative risk of having a stroke within a 3 year period for patients taking the new drug compared to warfarin?

Which one of the following statements best describes a type I statistical error?

A new test to screen for ovarian cancer in patients with a positive family history is tested on 920 patients. The test is positive in 16 of the 20 patients who are proven to have ovarian cancer. Of the remaining patients, only 10 have a positive test.

What is the negative predictive value of the new test?

A cohort study is designed to look at the association between working long hours and blood pressure.

The following results are obtained after 10 years of follow-up:

What is the odds ratio of developing hypertension if you work more than 40 hours/week compared to people who work less than 40 hours/week?

Which one of the foThe odds ratio approximates to relative risk if the outcome of interest is rare llowing statements regarding odds and odds ratio is correct?

What is the correct formula to calculate the positive predictive value?

A randomised controlled trial is performed to look at a new drug to prevent hip fractures in postmenopausal women. Group A consists of 1,000 women who take the new drug whilst group B contains 1,400 women taking a placebo. The hip fracture rate in group A is 2% and in group B is 4%.

What is the number needed to treat to prevent one hip fracture?

A rapid urine screening test is developed to detect Chlamydia. A trial involving 200 men and women is performed comparing the new test to the existing NAAT techniques:

What is the negative predictive value of the new test?

A new blood test which can show signs of myocardial damage within one hour of the onset of chest pain is developed. In a trial of 100 patients presenting with chest pain, 40 of the patients are later proven to have had myocardial ischaemia by conventional troponin tests. Of these patients the new test was positive in 20 cases. The new test was also positive in 20 of the remaining 60 patients later shown to have a negative troponin.

What is the negative predictive value of the new test for myocardial ischaemia?

A new screening test is developed for colorectal cancer. It is a blood test which detects a protein; the higher the level of the protein, the more likely a patient is to have colorectal cancer. If the cut-off for a positive test is increased,

which one of the following will also be increased?

A small study is designed to look at the link between drinking alcohol and liver cirrhosis. One hundred patients with liver cirrhosis were questioned and it was found that 80 of them drank excessive alcohol. As a control, one hundred patients without liver cirrhosis were questioned and only 20 of these patients drank excessively.

What is the odds ratio of developing liver cirrhosis for people who drink excessively compared to those who do not?

A new anti-epileptic drug is trialled for children with absence seizures. There are 250 children in the control group and 150 children assigned to take the new drug. After 4 months 100 children in the control group had had a seizure compared to 15 children in the group taking the new medication.

What is the relative risk reduction?

A study looks at adding a new antiplatelet drug in addition to aspirin to patients who’ve had a stroke. One hundred and seventy patients are enrolled for the study with 120 receiving the new drug in addition to aspirin and the remainder receiving just aspirin. After 5 years 18 people who received the new drug had a further stroke compared to 10 people who just received aspirin.

What is the number needed to treat?

Which one of the following statements regarding the use of the p-value in statistical hypothesis testing is correct?

A new biochemical marker has been found which is increased in mothers who are carrying fetuses with Down’s syndrome. The new blood test is trialled in 1,000 women over the age of 35 years. Of these women 20 were found to be carrying a fetus with Down’s syndrome as assessed using standard measures. The new test was positive in 15 of the 20 cases but was also positive in 30 of the remaining 980 women.

What is the positive predictive value of the test?

What is the correct formula to calculate the negative predictive value of a screening test?
TP = true positive; FP = false positive; TN = true negative; FN = false negative

A study looks at the use of amoxicillin in the treatment of acute sinusitis compared to placebo. The following results are obtained:

What is the odds ratio a patient achieving resolution of symptoms at 7 days if they take amoxicillin compared to placebo? 

A study is performed comparing two chemotherapy regimes for patients with small cell lung cancer. The end point of the study is survival time. Which one of the following types statistical measures is it most appropriate to compare survival time with?

A contingency table is constructed for a new blood protein marker to screen for prostate cancer in men aged between 50 and 70 years:

What is the positive predictive value of the new test?

A randomised controlled trial compares two drugs used in the initial management of rheumatoid arthritis. After being assigned to the randomised groups a number of patients drop out due to adverse effects of the medication.

How should the data be analysed?

An endocrinologist performs a study to assess whether a patient’s HbA1c level is correlated to their LDL level. Assuming both HbA1c and LDL are normally distributed,

which one of the following statistical tests is it most appropriate to perform?

A study looks at the benefits of adding a new antiplatelet drug to aspirin following a myocardial infarction. The following results are obtained:

What is the number needed to treat to prevent one patient having a further myocardial infarction within 3 months? 

You are asked to design a study to assess whether living near electricity pylons is a risk factor for childhood leukaemia.

What is the most appropriate type of study design?

A new blood test is developed to screen for prostate cancer. Trials have shown it has a sensitivity for detecting clinically significant prostate cancer of 80% but a specificity of 60%.

What is the likelihood ratio for a positive test result?

A study looks at whether a new oral treatment for patients with heart failure can prevent hospital admissions.

When reviewing the data how should it be decided if the test was statistically significant?

A new adjuvant treatment for women with breast cancer is investigated. The study looks at the recurrence rate after 5 years. The following data is obtained:

What is the relative risk reduction?